It will sound a million times better (its what I have on mine and really does sound nice
) As for performance increase, your looking around 10ish bhp (give OR take) for the full turbo back system. As Rhyso said, it frees up mid range and will give you better throttle response. A larger CAI (cold air intake, induction kit, whatever you want to call it) will compliment the larger downpipe and as its less restrictive and allows the car the breath better.
